1. Field of the Invention
The present invention relates to a peripheral monitor for monitoring periphery of a vehicle that is used to prevent the vehicle running on a road from running into and colliding with any obstacle by measuring a distance to the obstacle existing in the periphery of the vehicle and warning the driver.
2. Description of Related Art
Hitherto, a peripheral monitor for monitoring periphery of a vehicle is mounted on the inside of a bumper cover of the vehicle. For mounting such a peripheral monitor, relative position and angle between an antenna and the bumper are gradually changed while being monitored on the basis of amplification degree of an amplifier for amplifying strength of signals received by the antenna, and the antenna is fixed at a position and angle where amount of signal reflected from the bumper cover is the smallest in quantity. (See the Japanese Patent Publication (unexamined) No. 2002-071788 (paragraph 0030 to 0038, FIG. 2) 1, for example).
However, the inventors found out through experiments that the quantity of transmitted waves having been emitted or radiated from the transmitting antenna, reflected from the bumper and received by the receiving antenna fluctuates depending upon the quantity of foreign substance such as water drop, water film or dirt sticking onto the surface of the bumper.